Crankshaft bolt failure

Sadly this is a known error in the manual. Should be 25lb.ft. Norvil should place a note in the packet of bolts in my view - but this way they sell twice as many.

Also don't do as I did - do as I've since been told - run the nuts up first on the bench so you get a smooth torque without too much stick-slip.

I also didn't realise when I reassembled my crank that two of the stud holes are bored to tolerance of dowels. Don't know what effect it has if you put the wrong bolts in the wrong holes in the wrong order - maybe some real expert on this site does?

BUT - I wonder how many Norton cranks are split unnecessarily? Has anyone out there ever seen a 'sludge trap' with much more than a couple of millimetres of stuff in it? And since most cranks don't have one, then surely once it becomes 'brim full' it becomes like any other vehicle's crank and won't try to overfill itself until it clogs. My theory is (especially now we've all been using modern oils for decades) that lots of us make work for ourselves by splitting cranks for no good reason.

Norton engines have gone 'bang' for all sorts of reasons - but usually for over-revving or lack of oil - has anyone ever experienced failure because of a blocked 'sludge trap'? The words are merely a description of the effect they have - not of some clever design intent. Yes - they do trap sludge - just like dead ends in domestic plumbing systems - but so what?

hello send them back to Norvil and tell him this bolts are rubbish , they should of with stud 40lb foot pounds with ease ,this is what I have been trying to say were all being ripped off with unfit parts, and someone life maybe at stake at sometime, trading standards need to be told there ! Yours AJD

We found lots of sludge ina Dommi 99we did recently, well it was sludge once I guess, but it had hardenedinto a lookalike sintered block and the crank cheek was bonded to the flywheel with it.

Anna - don't blow a fuse! They are only little 5/16 bolts. Norvil aren't out to get you personally - yet! The book says 35 - I was suspicious since this was a lot more than the guide value on the printed plate on my old torque wrench. A quick Google search turned up this:

http://www.engineershandbook.com/Tables/torque.htm

I should have trusted the 'feel' of the spanner. The Norton book (Neil) just says to tighten them up and stake or tab plate. No mention of the mania for using torque figures - which are very untrustworthy anyway.

Thanks, Mark - I had a solid block in mine - but not as deep as the 'trap'. But centrifugal force put it there in a region of no flow. But has anyone had blocked oilways because of it?

If you haven't cleaned out the sludge trap, I would definitely recommend doing it if you've got the crank cases apart. I nearly didn't bother on a Commando engine I rebuilt, as it all looked in good condition. It was on the bench so I may as well split it. I didn't think there'd be much in there but it was solid with it like Mark's Dommie. You cannot justignore it, it will eventually block and stop the oil feed to the bigends.

The crank bolts should be replaced in the order they came out and new tab washers fitted, or if you haven't got them you can punch the side of the bolt end.

I once stripped a crank and the oil feed to the drive side big end was reduced to a worm hole through the sludge. Always strip a crank you have just bought!

I'm sure we stopped at 20lbs ft when retightening with new studs as it felt right then got the 'feel' with a spanner on themand then didthe bottom ones up as we couldn't get a torque wrench on those. Bottom ones are tabbed and loctited theothers loctited and centre punched.

As for splitting the crank if it's down that far anyway I don't think I couldn't now having seen what we found in there. It was a 'new' to me crank though. The evidence points to the bike, 58 Dommi,having stood for a long time, used again then stood for another long time. The sludge evidence waslike growth rings of a tree.

Thanks, Gordon and Mark. Sad news! Anyway - mine had 'only' done about 20000 miles when it was stripped, and the maximum amout of sludle was maybe 1/8 inch.

The biggest issue I had (apart of course from breaking my bolts by overtorque! - Mark did the right thing I'm now sure) was to find a way to safely mount it in a vice to remove the nuts. Maybe they were loctited or even glued. It was like trying to unbolt an eel.

I agree with David, don't blame Norvil (or any supplier) if a bolt breaks tightening it nearly 50% more than it is suppose to be. I agree, it might be nice to have a note included with torque specs, but where do you stop? Thats what the proper manual is suppose to be for. Mick Hemmings engine video is something everyone should watch before doing an engine strip,excellentinfo, and a torque wrench is seldom used in it.

We have all learned some Norton lessons the hard way Steve, now you have learned the old "Haynes manual torque lie" lesson, pass it on to others.

Skip

Many modern bolts in machines and steel structures are taken right up to their plastic strain limit. And steel can't do that many times before it gives up (low cycle numbers, high stress fatigue). Properly preloaded bolts should not see any fatigue cycles at all no matter how many load cycles occur unless the faying surfaces actually start to separate. Hopefully that should not happen in a Norton crank...

So the 6000 cycles per minute don't count - just the one plastic stress cycle of tightening it in the first place.

As we probably mostly know, modern car cylinder head bolts are tightened by 'part turn' to make them reach plasticity (yield) - (i.e. make them tigh and then turn them by some large enough angle to make them yield) so they sit there forever carrying stress equal to their elastic limit. But that's OK because until the head lifts off the block the stress never changes because the bolt length does not change until the surfaces come apart. If the head is take off, you must buy new bolts. Often these are waisted so the stretch is in the shank where it is safer than in the threads where most bolts stretch.

A better design would have 'waisted' bolts - just like big end cap bolts. But weight is vital with big end bolts so they spent money on flashy parts. In a crank shaft flywheel a bit of extra mass is perfectly acceptable so presumably they worked out that fairly crude bolts would suffice.

The trouble with measuring length for a bolt without a waist is that the stretch isn't even nearly uniform along the length of the bolts.

David Cooper.

It's bad enough Haynes have got this torque figure wrong with all the copies of that manual that have been sold, but for the tech section of the NOC to get is wrong as well is not good

As time marches on the more bad I hear and see about Norvil and presently I would not go near them or their parts. Andover Norton has some sharp individuals at it's helm and I believe makes the effort to supply superior parts that are at least OEM specification.

The original Norton factory recommended checking the sludge trap on engine tear-downs no matter the mileage. The 850 Commandos with the spin-on filters will have very clean sludge traps and nicer than average crank journals almost every time, but the older bikes will all have build-up and rod journals which have been noticeably scored from bits of metal that has gotten between the bearing shells and journals. The shells themselves will be full of metal particles embedded in the soft metal layer of the shell bearings on the early bikes, where on 850s some of the shell bearings will look so good you will be tempted to use them over again.

I like Mr. Marshall's engineering data for bolt torque. Every mechanic should get their hands on an old automobile engine before it is taken to a scrap yard and torque all the bolts on it until they break, just to get to know what tightening a bolt feels like as it gets tighter then begins to yield then finally fails. If you do this enough times and also have a natural mechanical aptitude then someday when you are in a bind or it suits the situation you may be able to tighten most fastners on most machinery competently without a torque wrench.

Previously wrote:

Anna - don't blow a fuse! They are only little 5/16 bolts. Norvil aren't out to get you personally - yet! The book says 35 - I was suspicious since this was a lot more than the guide value on the printed plate on my old torque wrench. A quick Google search turned up this:

http://www.engineershandbook.com/Tables/torque.htm

I should have trusted the 'feel' of the spanner. The Norton book (Neil) just says to tighten them up and stake or tab plate. No mention of the mania for using torque figures - which are very untrustworthy anyway.

Thanks, Mark - I had a solid block in mine - but not as deep as the 'trap'. But centrifugal force put it there in a region of no flow. But has anyone had blocked oilways because of it?

hello TODAY i have torqued up a 5/16th nickel plated nut and bolt in the vice to well over 40foot pounds and it did not break ! This Bolt And Nut Were Cycle thread just your every day nut and bolt , not a crankshaft bolt , I will try out a old crankshaft bolt I have And we will see the breaking point , more tomorrow

If you need to torque up the nuts on the studs that you can't get to on a Norton crank, you can use a standard 1/4 whit combination spanner and put your 1/2" square drive torque wrench on the open ended end. By maintaining the angle between the torque wrench and the spanner at 90 degrees you will excert whatever your torque wrench is set to on the nut. It doesn't matter how long the spanner is.

I tried the above method once on a crankshaft and discovered that some of the nuts appeared to still be a little slack. I consulted a university lecturer who taught Mechanical Engineering and he demonstrated through the use of vector diagrams that this method is only successful if the torque wrench is accurate, there is zero friction in the wrench and little stiction between the nut and stud threads.

He showed me an alternative spanner and torque wrench method which I used from then on for each of my crankshaft rebuilds. There is still an element of guessing as to the true torque setting but I have never lost a crankshaft subsequently.

He started by mounting a 5/16" bolt in a vice and then torquing a nut down on it to 24ft lb using a socket and torsion bar type of torque wrench. He then removed the 5/16" socket and replaced it with the combination spanner so that spanner and wrench were all in a near straight line. This set-up was then used very gently on the the nut until it just began to move. The torque required to do this being noted. In this case it was between 15 & 16 ft lb but will vary according to the length of combination spanner used.

To prove that this method did the job reasonably accurately, the crankshaft flywheel was mounted in the vice and the various nuts, bolts and studs all added to a firm tightness. The torque wrench was then used to tighten down the accessible nuts to 24 ft lb and then the spanner/wrench combination to set the others. Finally the torque wrench was used again on the first nuts to set them at 25 ft lb.

A couple of other points I would add from experience. Firstly, I recall, in the 70s,pulling a cricket ball lump from out of one crankshaft due to cheap oil being used in the engine. I always check the trap when stripping an engine that I have not serviced before.Modern oils don't seem to cause problems in the sludge trap that used to happen.

Secondly, I generally re-use as many of the original crankshaft bolts, nuts and studs as I can as I just do not trust the quality of many of the spares on the market. Unless the engine has been hammered a lot, I generally have found most of the threads ok.

Lastly, 5/16" bolts that tolerate 40 ft lb of torque must be very special. I have met dozens of people, who like myself, were too lazy to adjust down the wrench setting, from 30 ft lb, when doing up the cylinder head bolts and consequently fractured one of the front 5/16" studs or stripped the thread. You don't make that mistake too often!!!

I have only ever used the 'feels about right' method. The secret, if secret it is, is to use the appropriate length of spanner. Too long and you will over-torque. Of course there are plenty of people who could strip any thread, shear any bolt this way...

Previously wrote:

While I hear what David is saying concerning engines/structures using bolts which are designed to be near their elastic limit, I don't think that would apply to a 1961 Norton, except just maybe the big-end bolts. I suspect that a bolt which is tightened to only 60% of its ultimate yield strength could be torqued up and loosened 50 times without stretching measurably, and that might have been the reason that the 60% figure was chosen as a rule-of-thumb by those horny handed engineers of yore.

I might just get around to testing this hypothesis using the original flywheel bolts and report back to the forum.

An easy way to have a 5/16" HT bolt to not yield at 40 ft lb is to torque it up completely dry (thread might well strip though). I bet you could not do it with the thread well greased up with molybdenum grease.

I do feel tempted to just put back the apparently perfect original bolts. An owner who converted it to single carb can't have been that much of a thrasher.

I made up an adapter out of £2 combi from eBay and a part from an old socket set as attached pic and angled it at 90 degrees. Snap-On make something like this, but probably not in WW sizes.

Steve - I agree - I'm sure you are correct and Norton didn't expect the crank shaft bolts to go as far as yield. If they did, they would not have needed tab washers (except in aircraft...)

Having said that - if the cheeks of the crank do not come apart then the bolts do not fatigue so they should be safe to re-use, theoretically. I certainly intended to re-use mine - until I was idiot enough to follow an excessive torque figure instead of trusting my own judgement and to break the d**** things.

If cranks regularly separated then that would clean the sludge trap, wouldn't it? But fatigue life would be miniscule so it would never last long enough to get clogged up in the first place.

The reason for the use of 'one shot' yielded bolts is that the really important thing to control is the material properties - which is done in the laboratory and the steelworks - and not the vagaries of blokes like us.

One of our problems is that all we can do is guess what the designers intended.

Steve, David was sayingabout structures using bolts torqued up to their PLASTIC limit - that's the point beyond which there is yield but no recovery. As a retired Civil Engineer I would just say that structures are probably not a good example when talking about mechanical equipment because they are essentially static, although they have an element varying thermal and dynamic loading. I would never want an enginebolt to go beyond its ELASTIC limit. I expect Anna would concur with me on this.

I would say that anyone who splits a crank and doesn't renew all the nuts and bolts is taking economy too far. It's not as if you do it once a year even! Those, and big end bolts, should always be renewed. Andover Norton is obviously the place to buy them. See their section on "Pirate Parts" whichfeature poor quality big end bolts with machine-cut threads instead of the correct and much harder rolled threads. A-N's bolts are forged, not turned from oversized bar.

As anecdotal evidence I can quote an example of failure to renew big end bolts & nuts. A friend working for the RAC had a callout to a broken Jaguar XJ6 on the M3 where the conrods had parted company and taken a trip through the ENGINE BLOCK! I believe (I should KNOW this! ) that the XK engine block is cast steel, not iron, so that was one engine not suitable for exchange! It had previously been overhauled using the old B/E bolts. A clear case of false economy.

Highly stressed boltswhich you only get sight of once in a blue moon should always be replaced with new where available. Always go for OEM rather than patternwhere possible. You know it makes sense!

Cheers, Lionel

Actually Steve, I think you are agreeing with me. If you don't take something apart then it should be OK to leave them but we're mainly talking about dismantling and reassembly, which any common sense shouldtell you that highly stressed bolts should be renewed. That's why I quoted the example of the Jaguar big end bolts. You won't be able to tell if bolts are fatigued, no matter how many times you test torque them - until they break through metal fatigue! That's usually a microscopic crystalline failure not visible with the naked eye.

High Strength Friction Grip bolts do have telltales so do notnecessarily require a torque wrench, but all these types of bolts are "one-shot". You don't reuse them. Ditto for "Nyloc" nuts. Ever had a propshaft fall off a car because the "professional" main agent reused the nuts? My brother did back in the late 70s on his Triumph 2.5 PI. Luckily it was at the differential end so the shaft just dragged along the road until he stopped! If it had been the front (gearbox) end it could have dug into the road and ripped off the rear suspension! I gave the dealers a right rollicking in the hope that they wouldn't put people's lives at risk like that again.

Cheers, Lionel

Previously David Cooper wrote:

Sadly this is a known error in the manual. Should be 25lb.ft. Norvil should place a note in the packet of bolts in my view - but this way they sell twice as many.

Also don't do as I did - do as I've since been told - run the nuts up first on the bench so you get a smooth torque without too much stick-slip.

I also didn't realise when I reassembled my crank that two of the stud holes are bored to tolerance of dowels. Don't know what effect it has if you put the wrong bolts in the wrong holes in the wrong order - maybe some real expert on this site does?

BUT - I wonder how many Norton cranks are split unnecessarily? Has anyone out there ever seen a 'sludge trap' with much more than a couple of millimetres of stuff in it? And since most cranks don't have one, then surely once it becomes 'brim full' it becomes like any other vehicle's crank and won't try to overfill itself until it clogs. My theory is (especially now we've all been using modern oils for decades) that lots of us make work for ourselves by splitting cranks for no good reason.

Norton engines have gone 'bang' for all sorts of reasons - but usually for over-revving or lack of oil - has anyone ever experienced failure because of a blocked 'sludge trap'? The words are merely a description of the effect they have - not of some clever design intent. Yes - they do trap sludge - just like dead ends in domestic plumbing systems - but so what?

Over the years I have rebuilt a good number of crankshafts. Most have just had a layer of hard sludge no more than 5mm thick on one side of the trap. However, in one I removed the equivalent of a cricket ball, in size. I can only assume that a previous owner had never done a proper oil change. Just kept topping up the oil tank whenever the level dropped.

Reflecting on the initial problem of broken bolts/studs. I have generally found that the 5/16 studs in the top of the barrel break if the torquing is anywhere near 30 ftlbs. Which is easy to do if you get distracted while cranking down all the 3/8" headbolts. The manual says 20 ftlbs max.